In the related art, compact fluorescent lamps having a flat, thin structure suitable for narrow spaces, such as lighting for showcases or under-shelf lights, have been used. In recent years, in place of the fluorescent lamps, an LED lamp with a cap having a flat, thin structure, which adopts a light-emitting diode, which is a solid state light-emitting device having a long life and low power consumption, as a light source, has been suggested.